This project emphasizes epidemiologic investigations of infectious diseases of particular interest to the research program of the Rocky Mountain Laboratory. Current investigations include a study of Colorado tick fever in the Northwest, the etiologic relationship of various spotted fever-group serotypes of human illness, and improvement in laboratory methods for diagnosis of rickettsial infections, particularly Rocky Mountain spotted fever. BIBLIOGRAPHIC REFERENCES: Philip, R. N., Casper, E. A., MacCormack, J. N., Sexton, D. J., Thomas, L. A., Anacker, R. L., Burgdorfer, W., and Vick, S.: A comparison of serologic methods for diagnosis of Rocky Mountain spotted fever. Am J. Epidemiol. 105: 56-67, 1977.